1. Technical Field
The subject matter described herein generally relates to systems and methods for performing echo cancellation in an audio communication system, such as a telephony system.
2. Description of Related Art
Acoustic echo is a phenomenon that occurs in audio communication systems, such as telephony systems, when speech generated by a remote or “far-end” speaker and played back over a local or “near-end” loudspeaker is picked up by a near-end microphone and transmitted back to the far end. The transmitted signal is a delayed version of the original, which causes the echo. The received far-end signal does not transfer directly from the loudspeaker to the microphone, but is subject to the environment in which the loudspeaker and microphone are located. This may include differing signal paths causing reverberation and spectral shaping. These effects are the transfer function between the loudspeaker and the microphone. Such transfer function is dynamic, as objects in the environment move or the loudspeaker and/or microphone change position.
Acoustic echo cancellation refers to a process by which the acoustic echo is modeled and then subtracted from the signal that is to be transmitted to the far end. Acoustic echo cancellation is traditionally performed using an adaptive filter to estimate the transfer function between the loudspeaker and microphone. Typically, the filter parameters of the adaptive filter are incrementally modified over time to account for changes in certain instantaneous statistics associated with the signal being played back over the loudspeaker and the signal received via the microphone. For such acoustic echo cancellers there is always a risk of divergence and the possibility of objectionable artifacts. Furthermore, for such acoustic cancellers, it is necessary to detect periods when the near-end and far-end speakers are talking simultaneously (a condition known as “double-talk”) and to stop updating the adaptive filter during such periods to prevent divergence.
The features and advantages of the subject matter of the present application will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.